Optical stack including reflective polarizer and quarter-wave plate on skin layer of absorbing polarizer

ABSTRACT

Optical stacks are described. In particular, optical stacks including reflecting-absorbing polarizers and quarter-wave plates are disclosed. The optical core of the optical stack—which includes a reflecting-absorbing polarizer with at least one skin layer including polarizing dye—may be co-extruded or co-stretched.

BACKGROUND

Reflecting-absorbing polarizers may be reflective polarizers thatinclude polarization-selective light absorbing elements, such asdichroic dyes. These polarizers may combine the functionality of areflective polarizer and an absorbing polarizer. In emissive displays,such as organic light emitting diode displays (OLED displays) theemissive display panel may have a highly reflective back substrate,reducing contrast in ambient viewing conditions. Circular absorbingpolarizers are typically included in these displays to reduce thereflection of ambient light. These polarizers are often thick andprovide noticeable color artifacts when viewed off angle.

SUMMARY

In one aspect, the present description relates to an optical stack. Inparticular, the optical stack includes an optical core having a topsurface and a bottom surface, the optical core including areflecting-absorbing polarizer having at least one skin layer positionednearer the top surface than the bottom surface, the at least one skinlayer including polarizing dye. The optical stack also includes aquarter-wave plate disposed directly on the bottom surface of theoptical core. The optical stack contains no polarizing-selectingelements outside of the optical core.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded elevation cross section of a reflecting-absorbingpolarizer.

FIG. 2 is an exploded elevation cross section of an optical stackincluding a reflecting-absorbing polarizer.

FIG. 3 is a cross section of an emissive display including an opticalstack including a reflecting-absorbing polarizer.

FIG. 4 is a cross section of an optical stack further including a linerwith adhesive.

FIG. 5 is a diagram illustrating several exemplary measurement anglesfor a display.

DETAILED DESCRIPTION

FIG. 1 is an exploded elevation cross section of a reflecting-absorbingpolarizer. Reflecting-absorbing polarizer 100 includes hybrid polarizerportion 110 including alternating layers of high index layer 112 and lowindex layer 114, and reflective polarizer portion 120 includingalternating layers of high index layer 122 and low index layer 124.Reflecting absorbing polarizer 100 also includes skin layer 130. Hybridpolarizer portion 110 and reflective polarizer portion 120 are shown asconnected with dashed lines to represent that they are typicallyconnected as a single film; however, they are represented spatiallyseparated for ease of illustration and identification of theirconstituent parts.

In the configuration shown in FIG. 1 , hybrid polarizer portion 110 maybe a multilayer reflective polarizer. In some embodiments, themultilayer reflective polarizer includes thermoplastic birefringentlayers. Within hybrid polarizer portion 110, at least some instances ofhigh index layer 112 may include absorbing polarizing elements. Theseabsorbing polarizing elements may be any suitable material that absorbslight of one polarization in favor of light having another polarization.In some cases these materials may be referred to as dichroic. In someembodiment, these absorbing polarizing elements may be dyes, including,for example, dichroic dyes. In some cases, all of the instances of highindex layer 112 may include absorbing polarizing elements. In someembodiments, the dyes or absorbing polarizing elements may beorientable, that is, when stretched, the absorbing polarizing elementsmay preferentially absorb polarizations that are parallel to the stretchdirection. If the layers include orientable thermoplastic layers, thethermoplastic layers may be oriented (i.e., stretched) in the same stepas orienting the absorbing polarizing elements. Depending on whether thematerials of the thermoplastic layers are positively or negativelybirefringent; that is, whether the index of refraction increases ordecreases along the stretch direction, the block axis attributed to thebirefringence in the alternating layers may be parallel or perpendicularto the block axis attributed to the absorbing polarizing elements. Lowindex layer 114 is instead substantially free of absorbing polarizingelements. Hybrid polarizer portion 110 both reflects certainpolarizations of light due to its in-plane refractive index differencesand absorbs certain polarizations of light due to its absorbingpolarizing elements.

Reflective polarizer portion 120 may also be a multilayer reflectivepolarizer. The high index and low index layers of reflective polarizerportion 120 are substantially free of any absorbing polarizing elements.In some embodiments, reflective polarizer portion 120 may be in manyaspects substantially the same film or have substantially the sameproperties as hybrid polarizer portion 110. For example, reflectivepolarizer portion 120 and hybrid polarizer portion 110 may have the sameor similar layer counts, total thicknesses, layer thickness profiles,and may use similar material sets. Because hybrid polarizer portion 110contains absorbing polarizing elements, however, hybrid polarizerportion 110 and reflective polarizer portion 120 will never beabsolutely identical. In some embodiments, the layer count, layerthickness profiles, packet number and configuration, and material setsmay be different between the hybrid polarizer portion and reflectivepolarizer portion. In some embodiments, the layer profiles of eachpacket may be specifically designed to optimize collimation or otherwiseselectively reflect high angle light preferentially transmit lightwithin a desired angular range.

Hybrid polarizer portion 110 is disposed on reflective polarizer portion120. In some embodiments, hybrid polarizer portion 110 is laminated oradhered to reflective polarizer portion by any suitable attachmentmethod, including optically clear adhesives, pressure sensitiveadhesives, or the like. Any adhesive may in some embodiments have anindex of refraction close to that of adjacent layers of both the hybridpolarizer portion 110 and reflective polarizer portion 120 to avoid orminimize refractive or Fresnel reflection effects. In some embodimentshybrid polarizer portion 110 and reflective polarizer portion 120 areoptically coupled. In some embodiments, hybrid polarizer portion 110 iscoextruded with reflective polarizer portion 120, and hybrid polarizerportion 110 and reflective polarizer portion 120 may be separated by athicker non-optical layer, such as a protective boundary layer (PBL). Insome embodiments, hybrid polarizer portion 110 and reflective polarizerportion 120 are separated by a thick or dimensionally stable layer toimprove warp resistance or other physical characteristics.

Skin layer 130 is disposed on hybrid polarizer portion 110, and, moreparticularly, on an external surface of reflecting-absorbing polarizer100. The skin layer, in some embodiments, is coextruded and costretchedwith the rest of reflecting-absorbing polarizer 100. Skin layer 130 maybe thicker than any of the alternating high index layers 112 or lowindex layers 114. In some embodiments, skin layer 13 may be between 0.5μm or 15 μm. Skin layer 130 may include polarizing dye. In someembodiments, skin layer 130 includes a similar dye loading (by volume)compared with the high index layers including polarizing dye withinhybrid polarizer portion 110. In some embodiments the dye loading may behigher or lower. In some embodiments, an additional skin layer may beprovided on the opposite surface of the reflecting-absorbing polarizer.

In some embodiments, reflecting-absorbing polarizer 100 includes hybridpolarizer portion 110 but not reflective polarizer portion 120. In otherwords, the reflecting-absorbing polarizer may be a single packetconfiguration, where absorbing polarizing elements are present in all ofthe high index layers.

FIG. 2 is an exploded elevation cross section of an optical stackincluding a reflecting-absorbing polarizer. Optical stack 200 includesoptical core 210 having top surface 212 and bottom surface 214. Opticalcore 210 includes a reflecting-absorbing polarizer with alternatinglayers 215 and 216 and skin layer 218. The reflecting-absorbingpolarizer may also include an optional additional layer 220.Quarter-wave plate 230 is disposed directly on the bottom surface of theoptical core. Optionally, optical stack 200 includes bottom protectivelayer 240 and top protective layer 250.

Optical core 210 may be or may essentially be a reflecting-absorbingpolarizer. In this embodiment, the reflecting absorbing polarizerincludes alternating low index layers 215 and high index layers 216. Insome embodiments, the reflecting-absorbing polarizer may have adual-packet configuration as shown in FIG. 1 , or it may have a singlepacket configuration as described elsewhere. In any event, at least someof high-index layers 216 include polarizing dyes. Optical core 210 has atop surface 212 and a bottom surface 214 which may or may not becoincident with the top and bottom surfaces of the reflecting-absorbingpolarizer. Optical core 210 further includes top skin layer 218, which,as described in conjunction with the exemplary reflecting-absorbingpolarizer configuration in FIG. 1 , includes polarizing dyes. In someembodiments, optional additional layer 220 is included.

In some embodiments, optional additional layer 220 is an additional skinlayer. The skin layer may or may not include polarizing dyes. In termsof composition, thickness, and other physical properties, thisadditional skin layer may be similar to or different from skin layer218. In some embodiments, optional additional layer 220 is an immiscibleblend of two polymers, where at least one of the polymers is capable ofdeveloping birefringence when stretched. For example, optionaladditional layer 220 may be a diffuse reflective polarizing layer, suchas those described in U.S. Pat. No. 6,179,948.

In some embodiments, optional additional layer 220 is an adhesive. Insome embodiments, optional additional layer 220 is a pressure sensitiveand/or optically clear adhesive. Further, and as its name implies, insome embodiments, optical stack 200 may not include optional additionallayer 220 at all. For this reason, bottom surface 214 may be, in someembodiments, where it is illustrated in FIG. 2 , but may be, in otherembodiments, on the bottom surface of optional additional layer 220(instead of on the bottom surface of one of the alternating high or lowindex layers).

The optical core may be coextruded and cast together, as from afeedblock, for example. In some embodiments, one or more layers may becoated or laminated after extrusion, and stretched together. Theseprocesses may provide excellent material uniformity and consistencythroughout the film and make the challenge of laminating layers suchthat the optical axes are properly aligned a non-issue.

Quarter-wave plate 230 is directly disposed on bottom surface 214 ofoptical core 210. Quarter-wave plate 230 is configured to selectivelyretard incident light to convert it from linearly polarized light tocircularly polarized light (or elliptically polarized light) or viceversa. As is conventional, the quarter-wave plate is disposed such thatits slow axis at a 45 degree angle from the transmission axis of theadjacent polarizing elements, which may be optional additional layer 220configured as a diffuse reflective polarizer or the reflecting-absorbingpolarizer included in optical core 210.

Quarter-wave plate 230 may be any suitable construction. Generally, aquarter-wave plate includes a layer of a birefringent material. In someembodiments, quarter-wave plate 230 is liquid crystal polymer coated ona film or substrate, such as a cyclo-olefin polymer substrate, cellulosetriacetate (triacetyl cellulose, TAC), or polycarbonate. In someembodiments, as depicted in FIG. 1 , quarter-wave plate 230 may have aslow axis oriented substantially 45° to the transmission axis of thereflecting-absorbing polarizer included in optical core 210. For thepurposes of this application, an orientation of substantially 45° andsubstantially 135° may be considered substantially equivalent as betweentwo axes, given the bidirectional nature of a transmission axis.However, substantially 45° and substantially 135° may be used, whencomparing three or more axes, to distinguish two axes that may beoriented 90° to one another. Substantially 45° also may be understood tonot be limited to precisely 45°; instead, the alignment of the axes maybe within 10°, within 5°, or within 1° of 45°. Alignment may in somecases be a tradeoff between manufacturability (e.g., error tolerance)and optical performance, the appropriate balance being determineddepending on the desired application. Nonetheless, precise alignment maynot in fact be crucial in many applications. For purposes of thisapplication, the terms plate, retarder and retardation layer are usedinterchangeably.

In some cases quarter-wave plate 230 may be achromatic. In other words,quarter-wave plate 230 may rotate or modulate polarization the same,independent of the wavelength of incident light.

Achromatic quarter-wave plate may be used in some embodiments tocompensate for the non-linear wavelength-dependent modulation of lightin a conventional quarter-wave retardation layer, making thetransmission instead relatively flat, linear, or in conformance with orapproaching any desired spectrum. This may minimize or eliminate shiftsin color or other artifacts. In some embodiments the desiredachromaticity may be achieved through designing or selecting certainwavelength-specific retardance. For example, the achromatic quarter-waveretarder may have a retardance (i.e., difference in path length of oneof the orthogonal field components of incident light) of 100 nm for 400nm light and 200 nm for 800 nm light (corresponding to a quarter awavelength). However, precise linear achromaticity is not necessary insome embodiments, and therefore the actual retardance values may bewithin 10%, within 7.5%, within 5%, or within 2% of the quarterwavelength value.

In some embodiments, the reflecting-absorbing polarizer may be turned,through judicious selection of materials and layer thickness of opticalrepeat units, to compensate for the wavelength-dependent modulation of aconventional quarter-wave retardation layer. In other words, the tunedreflective polarizer may be tuned to compensate for or reduce theperceived effect of wavelength dispersion of the quarter-waveretardation layer. The optical thickness (physical thickness multipliedby the refractive index of a material) of each set of microlayers,called an optical repeat unit, reflects light at wavelengths about twiceits optical thickness through constructive interference. In designing atuned reflective polarizer, the arrangement of these layers may beutilized to provide greater or lesser reflection based on wavelength.

Bottom protective layer 240 and top protective layer 250 are optionallyincluded in optical stack 210 and may have similar compositions andproperties or they may be different. Although characterized asprotective layers, they may serve other functions instead of or inaddition to protection of the layers of the optical stack. For example,one or more of the protective layers may include a surface or bulkdiffuser. Any appropriate diffusing structure may be used. In someembodiments, bottom protective layer 240 or top protective layer 250include a microreplicated surface structure that provides surfacescattering. In some embodiments, the protective layers include particlesor beads that provide bulk or volume scattering. In some embodiments,both types of scattering are provided by the protective layers,sometimes in a single layer.

In some embodiments, the protective layers may impart warp, thermal, orscratch/abrasion resistance, or they may provide any other physical orenvironmental advantage or characteristic to optical stack 210. In someembodiments, the protective layers may provide anti-wetout, anti-Newtonring, or slip characteristics. One or both of the protective layers maybe peelable or strippable, which may provide beneficial handlingcharacteristics to the film through the manufacturing, converting, andassembling process. In some embodiments, the protective layers may be,include, or function as hardcoat layers, with any suitable or desirablepencil hardness, for example.

Conventional circular absorbing polarizers usually include generallythick dye-stained polyvinyl alcohol (PVA) carrier layers. At least oneTAC layer is also often utilized in order to protect against degradationof the stained layer. These layers may add about 50-75 micrometers ofthickness, if not more.

FIG. 3 is a cross section of an emissive display including an opticalstack including a reflecting-absorbing polarizer. Emissive display 300includes optical core 310 with top surface 312 and bottom surface 314and including alternating layers 315 and 316 and skin layer 318. Quarterwave plate 330 is disposed directly on bottom surface 314 of opticalcore 310. Emissive display panel 360 is disposed nearer bottom surface314 than top surface 312.

Emissive display panel 360 may be any suitable emissive display panel.Emissive display panel 360 may be full color or, in some embodiments,emissive display panel 360 may be monochrome. In some embodiments,emissive display panel 360 includes one or more light emitting diodes(LEDs). In some embodiments, the emissive display panel may include oneor more organic light emitting diodes (OLEDs). In some embodiments, theemissive display panel may include a plasma display. These emissiveelements may produce light of any wavelength or any combination ofwavelengths. In some embodiments, the wavelengths generated by theemissive materials may be selected to appear white or, throughcombinations of colors, to reproduce to a human observer anappropriately wide color gamut. Emissive display panels aredistinguished by non-emissive display panels in that emissive displaypanels display an image substantially directly; in other words any imagefrom emissive display 300 is substantially related to the image patternon the emissive display panel. Non-emissive panels, such as a typicalliquid crystal display (LCD) panel, use selective light gating throughelectrical control of the liquid crystal material to form images fromotherwise substantially uniformly illuminated backlights. Emissivedisplay panel 360 should be understood to also include all appropriateand suitable driving electronics. In some embodiments, emissive displaypanel 360 may be an active-matrix OLED, or AMOLED system.

The other components in emissive display 300 shown in FIG. 3 are asdescribed in, for example, FIG. 2 . Emissive display 300 may include anyor all of the optional protective layers described in FIG. 2 , which arenot shown again in FIG. 3 for simplicity of illustration.

FIG. 4 is a cross section of an optical stack further including a linerwith adhesive. Optical stack 400 includes optical core 410 with topsurface 412 and bottom surface 414 and having alternating layers 415 and416 and skin layer 418. Quarter-wave plate 430 is disposed directly onbottom surface 414. Liner 470 is attached to the bottom surface of therest of the optical stack via adhesive 472.

Optical stack 400 may be formed through a continuous roll-to-rollprocess. In a roll of film including optical stack 400, certainprotection for the components of the optical stack may be needed duringwinding, handling, unwinding, and possibly converting.

Liner 470 may be any suitable liner, and may be selected for itsphysical characteristics. For example, liner 470 may prevent damage toquarter-wave plate 430 by scratching or rubbing, or it may protect theaccumulation of dirt, dust, or other debris within the optical stack. Insome embodiments, liner 470 may be selected for its optical properties.For example, liner 470 may absorb UV light that may be damaging to therest of optical stack 400. Liner 470 is shown on only the bottom side ofoptical stack 400, but in some embodiments, liner 470 is on both sides.In some embodiments, only one side is needed as the liner is intended asprotection as optical stack 400 is rolled on itself. Liner 470 is nottypically intended to remain on optical stack 400 in its final displayapplication. For that reason, liner 470 may be selected to haveappropriate structural integrity or tear resistance, such that theentirety of liner 470 can be removed, either on an individual convertedpiece or as part of a continuous process.

Adhesive 472 may be any suitable adhesive and may be chosen for itssuitability as a cleanly removable adhesive. Adhesive 472 may be orinclude a pressure sensitive adhesive. In some embodiments, adhesive 472may be a stretch releasable adhesive. In some embodiments, adhesive 472may be a repositionable adhesive.

EXAMPLES Example 1

An integrated absorbing-reflective polarizer was prepared as follows. Asingle multilayer optical packet was co-extruded as described in US2011/0102891 (“Low Layer Count Reflective Polarizer with OptimizedGain”) with the following exceptions. The first optical layers werecomprised of a blend of polyethylene naphthalate (PEN) homopolymer (100mol % naphthalene dicarboxylate with 100 mol % ethylene glycol) having aTg of 121-123 degrees centigrade and four different dichroicco-extrudable absorbing dyes (PD-325H, PD-335H, PD-104 and PD-318H; allavailable from Mitsui Fine Chemicals, Tokyo Japan), as described in WO2014/130283. The dye weight percentages were as follows: PD-325H=1.67 wt%, PD-335H=0.21 wt %, PD-104=0.67 wt %, and PD-318H=1.25 wt %. Thesecond polymer (second optical layers) was a blend of polycarbonate andcopolyesters (PC: coPET) such that the index was about 1.57 and remainedsubstantially isotropic upon uniaxial orientation. The PC: coPET molarratio was approximately 42.5 mol % PC and 57.5 mol % coPET and had a Tgof 105 degrees centigrade. The polymer used for the layer opposite thecasting wheel was a blend of 90/10 coPEN, a polymer composed of 90%polyethylene naphthalate (PEN) and 10% polyethylene terephthalate (PET).The polymer used for the layer facing the casting wheel was a blend ofpolyethylene naphthalate (PEN) homopolymer (100 mol % naphthalenedicarboxylate with 100 mol % ethylene glycol) having a Tg of 121-123degrees centigrade and four different dichroic co-extrudable absorbingdyes (PD-325H, PD-335H, PD-104 and PD-318H), as previously described.The dye weight percentages utilized for the layer facing the castingwheel were as follows: PD-325H=0.93 wt %, PD-335H=0.35 wt %, PD-104=0.56wt %, and PD-318H=0.41 wt %.

The materials were fed from separate extruders to a multilayercoextrusion feedblock, in which they were assembled into a packet of 305alternating optical layers. The skin layers of the first optical layermaterial were added to the construction in a manifold specific to thatpurpose, resulting in a final construction having 307 layers. Themultilayer melt was then cast through a film die onto a chill roll, inthe conventional manner for polyester films, and quenched. The cast webwas then stretched in a commercial scale linear tenter at temperaturesand draw profiles similar to those described in Example 2 of US2007/0047080. The film thickness, measured with a capacitance gauge, wasapproximately 43 micrometers.

Next a circular polarizer (CP) was made utilizing the integratedpolarizer. Materials were solvent coated and UV cured on the integratedpolarizer with the slow optical axis oriented at 45 degrees relative tothe pass direction of the integrated polarizer. The coated layer had aretardation of 138 nm at a wavelength of 550 nm. (Retardation is definedby Re=(ni−nj)*d, where ni−nj is the in-plane birefringence differencebetween the slow and fast optical axis of the coated material and d isthe thickness of the coated layer.) The coating materials utilized werematerials similar to those described in US2002/0180916, US2003/028048and US2005/0072959 where the linear photopolymerizable polymer (LPP)material was ROP-131 EXP 306 LPP and the liquid crystal polymer (LCP)material was ROF-5185 EXP 410 LCP (both available from RolicTechnologies, Allschwil, Switzerland). The corresponding integrated CPhad a thickness of about 44 μm. The integrated CP was then laminatedwith optically clear pressure sensitive adhesive (OCA) to an OLEDdisplay (SAMSUNG GALAXY S 5, available from Samsung Electronics, Suwon,South Korea, and LG G FLEX, available from LG Corp., Seoul, South Korea)where its color performance was measured with an Eldim L80Spectraradiometer (available from Eldim, Herouville-Saint-Clair,France). To determine color change as a function of viewing angle indisplay 510, color measurements were taken on-axis 520 n (normalincidence) and at 60 degrees off-axis 520 o (oblique incidence) relativeto the display normal, as shown in FIG. 5 . Measurements were taken atvarious points from 0 to 135 degrees azimuthally, at 45 degreeincrements, and averaged.

The brightness and reflectivity were also measured for theintegrated-CP. These are shown in Table 2. Brightness was measured viaPR-650 Spectrophotometer (available from Photo Research Inc., ChatsworthCalif.) and reflectivity was measured via Lambda 900 Spectrometer(available from Perkin Elmer, Waltham Mass.). To measure the brightness,the OLED device with integrated-CP made as described above was laminatedusing OCA to a white screen and the PR-650 was adjusted until thepicture was focused on the pixels of the OLED device. The PR-650 thenmeasured the brightness in Cd/m{circumflex over ( )}2. For reflectivitymeasurements, the first step was to auto-zero the equipment using areference mirror standard; the mirror was placed facing the port openingof the Lambda spectrometer and the percent reflectance was measured.After the auto-zero was complete, the OLED device with integrated-CP waslaminated, using OCA, to the encapsulation glass, placed facing the portopening and the percent reflectance was measured and normalized to thestandard mirror. The OLED-CP thickness values were obtained by SEMcross-section of the SAMSUNG and LG devices as received.

TABLE 2 Brightness, Reflectivity, Average change in color coordinatesu′, v′ and thickness (in micrometers) for OLED-CP's. OLED-CP % ThicknessBrightness Reflectivity Avg Δu′v′ color Sample (μm) (cd/m²) (% T) (60deg) change SAMSUNG GALAXY S 5 Samsung 175 337.9 5.59 0.0176 0 GalaxyS5 - as received Comparative 320 326.5 5.94 0.0122 30.7 Example 1Comparative 360 484.9 15.63 0.0103 41.5 Example 2 Example 1 44 194.711.31 0.0142 20 Example 2 154 200.3 11.02 0.0148 16 Example 3 48 245.27.29 0.0091 48.3 Example 4 165 248.3 6.61 0.0089 49.4 Example 5 47 244.912.66 0.0115 34.7 Example 6 170 245.6 11.80 0.0084 52.3 Example 7 45288.5 8.54 0.0083 52.8 Example 8 171 279.8 8.50 0.0068 61.4 LG G FLEX LGFlex - as 210-278* 297.5 6.36 0.0379 0 received Comparative 320 288.46.26 0.0264 30.3 Example 1 Comparative 360 458.4 20.10 0.0230 39.3Example 2 Example 1 44 177.3 11.45 0.0242 36.1 Example 2 154 173.3 11.260.0179 52.8 Example 3 48 219.5 7.60 0.0268 29.3 Example 4 165 222.1 7.960.0268 29.2 Example 5 47 221.8 16.22 0.0210 44.6 Example 6 170 223.513.25 0.0247 34.8 Example 7 45 257.4 8.25 0.0257 32.1 Example 8 171248.5 8.34 0.0288 24.0 *LG G FLEX OLED-CP possessed additionalpotentially non-optically functioning layers that may be OCA

Example 2

The integrated absorbing-reflective polarizer of Example 1 was used tomake a circular polarizer. The integrated polarizer film was laminatedwith an optically clear pressure sensitive adhesive (OCA) to a quarterwave plate (QWP) with trade name APQW92-004-MT (available from AmericanPolarizers, Inc., Reading, Pa.). The QWP optical axis was approximately45 degrees relative to the optic axis of the integrated polarizer. Thethickness of the QWP was 110 μm. The integrated-CP was then laminatedwith optically clear pressure sensitive adhesive (OCA) to the OLEDdisplays where its brightness, reflectivity, color performance, andthickness were measured as previously discussed and reported in Table 2.

Example 3

The birefringent integrated absorbing-reflective polarizer was preparedthe as in Example 1 except that the cast web was then stretched in aparabolic tenter using an unconstrained uniaxial stretch so that thefilm is allowed to] contact or relax substantially equally in the y andz directions while being stretched in the x direction. The temperaturesand draw ratios used were similar to those described in Example 2 ofU.S. Patent Publication 2007/0047080. The transverse direction (TD) drawratio was measured to be 6.0× while the downweb or machine direction(MD) draw ratio was measured to be 0.48×.

To create a circular polarizer utilizing the integrated polarizer,materials were solvent coated and UV cured on the integrated polarizersimilar to that in Example 1. The corresponding Integrated CP had athickness of about 47 micrometers+1 micrometer for a total of 48micrometers. The integrated CP was then measured for brightness, colorperformance and reflectivity as in previous examples. The results areshown in Table 2.

Example 4

The integrated polarizer film of Example 3 was laminated with the sameQWP as in Example 2 to create the integrated-CP. The integrated CP wasthen measured for brightness, color performance and reflectivity as inprevious examples. The results are shown in Table 2.

Example 5

A birefringent integrated absorbing-reflective polarizer was prepared asin Example 1 with the following exception. The first optical layers werecomprised of a blend of 90/10 coPEN, a polymer composed of 90%polyethylene naphthalate (PEN) and 10% polyethylene terephthalate (PET),and four different dichroic co-extrudable absorbing dyes (PD-325H,PD-335H, PD-104 and PD-318H), as previously described. The dye weightpercentages utilized in Example 5 were: PD-325H=0.93 wt %, PD-335H=0.12wt %, PD-104=0.37 wt %, and PD-318H=0.69 wt %. The dye utilized withinthe first optical layers was approximately half of that used in Examples1-4. The integrated CP was then measured for brightness, colorperformance and reflectivity as in previous examples. The results areshown in Table 2.

Example 6

The integrated polarizer film of Example 5 was laminated with the sameQWP as in Example 2 to create the integrated-CP. The integrated CP wasthen measured for brightness, color performance and reflectivity as inprevious examples. The results are shown in Table 2.

Example 7

A birefringent integrated absorbing-reflective polarizer was prepared asin Example 5 except that the cast web was then stretched similar to thatin Example 3 but at a TD ratio of 6.0× and MD ratio of 0.46×. Theintegrated CP was then measured for brightness, color performance andreflectivity as in previous examples. The results are shown in Table 2.

Example 8

The integrated polarizer film of Example 7 was laminated with the sameQWP as in Example 2 to create the integrated-CP. The integrated CP wasthen measured for brightness, color performance and reflectivity as inprevious examples. The results are shown in Table 2.

Comparative Example 1

A two layer optical stack consisting of SanRitz 5618 H-Type polarizer(available from Sanritz America, Chula Vista Calif.), and the quarterwave film described in Example 2 was laminated at 45 degrees to the passaxis of the Sanritz polarizer. The three films were laminated togetherusing a 25 micrometer thick 8171 optically clear adhesive (availablefrom 3M Co., St. Paul Minn.). The film stack was measured as previouslydescribed for OLED performance and thickness. The results are shown inTable 2.

Comparative Example 2

A three layer optical stack was made. It consisted of APF-V3 absorbingpolarizer (available from 3M Co.), Sanritz 5618 H-Type polarizer, andthe quarter wave film of Example 2. The quarter wave plate was laminatedat 45 degrees to the pass axis of APF-V3 and the Sanritz polarizer. Thepass directions of the APF-V3 and Sanritz polarizers were aligned. The8171 optically clear adhesive, 25 micrometers thick, was again used tolaminate the three films together. The film stack was measured aspreviously described for OLED performance and thickness. The results areshown in Table 2.

The values presented in Table 2 for Examples 1-8 are consideredgenerally acceptable in terms of display performance attributes for anOLED device.

The following are exemplary embodiments according to the presentdisclosure:

-   Item 1. An optical stack, comprising:    -   an optical core having a top surface and a bottom surface, the        optical core including a reflecting-absorbing polarizer having        at least one skin layer positioned nearer the top surface than        the bottom surface, the at least one skin layer including        polarizing dye; and    -   a quarter-wave plate disposed directly on the bottom surface of        the optical core;    -   wherein the optical stack contains no polarization-selecting        elements outside of the optical core.-   Item 2. The optical stack of item 1, wherein all of the optical core    has been stretched together.-   Item 3. The optical stack of item 1, wherein all the optical core    has been coextruded.-   Item 4. The optical stack of item 1, wherein the    reflecting-absorbing polarizer includes a second skin layer    positioned nearer the bottom surface than the top surface.-   Item 5. The optical stack of item 1, wherein the optical stack    includes a diffuse reflective polarizing layer positioned nearer the    bottom surface than the top surface.-   Item 6. The optical stack of item 5, wherein the diffuse reflective    polarizing layer includes a first polymer and a second polymer, and    the first polymer and the second polymer are immiscible.-   Item 7. The optical stack of item 6, wherein at least one of the    first polymer and the second polymer is a birefringent polymer.-   Item 8. The optical stack of item 1, wherein the optical stack    further comprises at least one protective layer, but not in the    optical core.-   Item 9. The optical stack of item 8, wherein the at least one    protective layer includes a diffusing surface structure.-   Item 10. The optical stack of item 8, wherein the at least one    protective layer includes a bulk diffuser.-   Item 11. The optical stack of item 1, wherein the optical stack    further comprises at least two protective layers, but not in the    optical core.-   Item 12. The optical stack of item 1, wherein the optical core    together with the quarter-wave plate has a total thickness of no    more than 100 micrometers.-   Item 13. The optical stack of item 1, wherein the optical stack has    a total thickness of no more than 100 micrometers.-   Item 14. An emissive display comprising at least one light source    and the optical stack of item 1, wherein the optical stack is    disposed such that the bottom surface of the optical core is    positioned nearer the at least one light source than the top    surface.-   Item 15. The optical stack of item 1, further comprising a layer of    optically clear adhesive and a liner, wherein the optically clear    adhesive is disposed between the liner and the rest of the optical    stack.-   Item 16. A roll of film, comprising the optical stack of item 15.-   Item 17. The optical stack of item 1, further comprising a bulk    diffuser disposed on the top surface of the optical core.-   Item 18. The optical stack of item 1, further comprising a surface    diffuser disposed on the top surface of the optical core.-   Item 19. The optical stack of item 1, wherein the    reflecting-absorbing polarizer comprises a plurality of alternating    first and second polymer layers, wherein the first polymer layer has    a higher index of refraction than the second polymer layer and the    first polymer layer includes polarizing dye.-   Item 20. The optical stack of item 1, wherein the    reflecting-absorbing polarizer comprises:    -   a reflective polarizer portion comprising a plurality of        alternating first and second polymer layers, wherein each of the        alternating first and second polymer layers is substantially        free of polarizing dye; and    -   a hybrid polarizer portion comprising a plurality of alternating        third and fourth polymer layers;    -   wherein the third polymer layer has a higher index of refraction        than the fourth layer;    -   wherein the third polymer layer includes polarizing dye; and    -   wherein the reflective polarizer portion and the hybrid        polarizer portion are disposed adjacent to one another.

Descriptions for elements in figures should be understood to applyequally to corresponding elements in other figures, unless indicatedotherwise. The present invention should not be considered limited to theparticular examples and embodiments described above, as such embodimentsare described in detail in order to facilitate explanation of variousaspects of the invention. Rather, the present invention should beunderstood to cover all aspects of the invention, including variousmodifications, equivalent processes, and alternative devices fallingwithin the scope of the invention as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A multilayer optical film comprising: a reflective polarizer comprising a plurality of alternating higher index first polymer layer and lower index second polymer layer, the first and second polymer layers substantially free of polarizing dye; an absorbing polarizer coextruded and costretched with the reflective polarizer and comprising a plurality of alternating higher index third polymer and lower index fourth polymer layers and at least one skin layer having a thickness between 0.5 microns and 15 microns, the third polymer layers comprising polarizing dye; and a quarter-wave plate coated directly on the at least one skin layer.
 2. The multilayer optical film of claim 1, wherein at least one of the first and second polymer layers is birefringent.
 3. An emissive display comprising: an organic light emitting diode (OLED) display panel; the multilayer optical film of claim 1 disposed on the OLED display panel so that the quarter-wave plate faces the OLED display panel. 